The invention concerns a universal joint for a cardan shaft suited for transmission of high torque.
Conventional universal joints for a cardan shaft are known, e.g., from
1) German Patent Document 36 44 204 C2; and PA1 2) British Patent Document 22 49 818 A.
When using cardan shafts suited for transmission of high torques in heavy machine construction, the universal joints--depending on the particular application--are exposed not only to high torques, but to a considerable extent also to transverse forces. Therefore, universal joints are equipped with radial bearings for transmission of peripheral forces and are equipped with axial bearings for absorption of transverse force. Generally, universal joints are supposed to possess, in addition to a high torque transmission capacity combined with a long bearing life, a minimal number of components of simple design and to involve low assembly expense. The transmission of high torques combined with a long bearing life presupposes the use of bearings with increased load capacity and, thus, larger bearing dimensions. These, in view of the limited space available, prove to be problematic.
From the German Patent Document 36 44 204 C2 it is previously known to relocate the axial bearing from its conventional location at the root of the journal to the end face of the journal, wherein the axial bearing bears on the radial bearing bush, which forms a unit with the journal, and on the inside surface of the bearing cap. The end face of the radial bearing bush is flush with the end face of the journal, i.e., it joins the end face of the journal in a plane, which further limits the construction space for the radial bearing, which in vertical direction is limited already by the design of the universal joint yoke and of the bearing cap.
The transverse force to be transmitted by the spider to the yoke, which with a respective angular position of the cardan shaft acts as an axial force in the direction of the journal axis away from the axis of the joint, extends from the end face of the journal through the inner race of the axial bearing and the axial bearing rollers to the other race to the bearing cap. The force, however, is not transmitted to the yoke of the universal joint along the shortest distance via the bearing cap, by means of screws, or via the shaft of the radial bearing outer race, by means of retaining rings, joined to the inside surface of the bearing cap. Rather, it is passed from the one bearing cap situated in the direction of force and not rigidly joined to the yoke half into the anchor joined to the bearing cap. The anchor is joined as well to the bearing cap on the opposite yoke half. The force bears there on the yoke with a working direction toward the axis of the joint. The bearing cap may bear also on the end face of the radial bearing outer race, provided the design of said race is such that it can be inserted from outside into the bearing bore up to a stop. Hence, a transverse force acting on the one bearing cap is not absorbed by that yoke eye against which the transverse force from the axis of the joint is directed, but by the opposite yoke eye. With this design of the universal joint, the loaded bearing is spared deformations in the area of the bearing bore in the yoke of the joint, thereby assuring optimum loadbearing performance in the axial bearing.
It is known that the length of the anchor is so chosen that both axial bearings will upon assembly of the caps to the anchor be subjected to a specific pre-stress. The pre-stress contributes to extensively avoiding, in the occurrence of a transverse acceleration without torque, axial backlash in the radial bearings in the direction of the journal axis, i.e., the relative movement of the anti-friction elements relative to the races of the radial bearing. With an axial force active, the anchor acts similar to an anti-fatigue-shaft bolt. Due to the force-dependent lengthening of the anchor, an axial displacement of the bearing cap in the eye of the yoke occurs in the working direction of the force, along the journal axis and away from the axis of the joint through the axial bearing. At the same time, the bearing cap which bears on the opposite yoke half is forced on the yoke eye, or respectively the yoke half. Owing to the axial displacement of the bearing cap, the contact pressure of the bearing cap on the opposite yoke half against the yoke of the joint, for introduction of the axial forces on the joint yoke, and due to the continual reciprocation of these operating conditions on one bearing cap, the end face and the inside surface of the bearing caps are exposed to heavy wear in the marginal regions. Contact corrosion, packing wear and frictional wear result in undesirable backlash.
British Patent Document 2 249 818 A teaches a universal joint design where the axial bearing is relocated from its conventional position of installation at the root of the journal, into a bore arranged on the inside of the journal. Arranging the axial bearing within the bore of the journal offers the advantage that the collar of the radial bearing bush can be made much longer, thereby gaining additional space for the anti-friction elements of the radial bearing. To assure an optimum load performance of the axial bearing, the bearing arrangement includes a backing ring which under load automatically adjusts elastically. With this design, the transverse and axial forces directed away from the joint axis are introduced in the yoke half at which the axial force also is directed. Disadvantages of this design include elevated expense of manufacture, assembly and maintenance, which expresses itself in increased cost. Also, achieving an optimum load performance of the axial bearing depends on the design of the backing ring.
The problem underlying the invention, therefore, is to provide a universal joint with a design such that the disadvantages of conventional designs will be avoided while achieving a reduction in number of components and assembly expense, as well as an increased bearing service life along with a simultaneous increase of the torques to be transmitted by the universal joint arrangement, by increased load capacity, especially of the dynamic load capacity, and thus an augmentation of the construction space available for the bearing. At the same time, the structural design is meant to be such that the axial forces will always bear on the yoke halves of the joint with a working direction toward the joint axis, that is, so that axial retainers for the individual bearing races will be dispensable and no force transmission elements will be necessary for transmitting the axial forces directed away from the joint axis along the shortest path to the yoke of the joint. This means that the axial force is introduced in the joint yoke always as a compressive force. The function guaranteed by the tie rod of DE 36 44 204 (transverse force support on the yoke half opposite the yoke half situated in the direction of force) and the specific pre-stress of the axial bearings is meant to be achieved through simpler design means, i.e., a universal joint design with fewer and more easily made components, which additionally allow an easier assembly. The wear occurring with conventional designs, due to axial displacement, on the end faces of the bearing caps and in the radial bearing is meant to be reduced.